Audiometers and Audiometric Testing Rooms: Calibration and Documentation

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Source: Workplace INTEGRA Associate

What does OSHA require regarding audiometer calibration?

The audiometer must function within certain tolerance limits in order to be considered as operating within the specifications set forth by OSHA.

Annually, OSHA requires the audiometer undergo an "acoustic calibration" whereby three functions are measured:  dB output levels, frequency characteristics, and volume control linearity.  In other words, the acoustic calibration answers the following questions: 

• 1) If the audiometer's volume control says X dB HL (60 dB HL, for instance) is it really producing an X dB HL signal?
• 2) Does the volume control work appropriately?
• 3) If the frequency control is set to a particular frequency (1000 Hz, for instance), is the audiometer actually producing that frequency?

Every two years, OSHA requires an "exhaustive calibration" which is an acoustic calibration plus a few more functions. As a practical matter, few perform acoustic calibrations as it requires not much more time to conduct an exhaustive calibration.

Where are acoustic and exhaustive audiometer calibrations conducted?

One method is to carefully box the audiometer and headphones, then ship to the manufacturer.  The major advantage of this method is that faulty internal components can be identified during the calibration and repaired using the manufacturer's parts.

A second method is similar to the first:  ship to a provider of calibration services.  If issues are uncovered that cannot be resolved (a rarity), the audiometer can be sent to the manufacturer.

A third method is to have a technician come on-site to perform the calibration.  There are two major advantages to this method.  First, no lost testing time associated with shipping the audiometer back and forth.  Second, the calibration is conducted with all of the connecting cables in place as one would ordinarily conduct a hearing test.  If the connecting cables or sound booth jack panel are causing issues, this can be determined during the calibration process and often resolved at the time.

What about daily listening checks? 

Just because the audiometer passed an acoustic or exhaustive calibration check seven months ago does not mean that is functioning properly today.  It is critical to conduct a daily listening check on the audiometer.  This is not difficult to do, requires only a few minutes, and need only be done on a day that audiometric testing will take place.  A daily listening check has two components:

Biological calibration check:  most with any experience doing industrial audiometric testing are familiar with bio-acoustic simulators often known as "Oscars" or "Bio-Bettys" or "Monitors".  One places the headphones on the simulator, gives the simulator a hearing test, and compares the result at each frequency to its baseline.  If the output is within ± 10 dB at each frequency for each headphone (left and right), then the audiometer is considered to be "in calibration."

Self-Listening check:  This can be performed either before or after the biological calibration check.  This is done because the bio-acoustic simulators do not know the difference between a nice, clean pure tone and various noises that can interfere with an actual test.  There is no need to do a full hearing test on yourself, just put the headphones on and check a few things.  Do the tones sound like tones?  Wiggle the cords, do you hear static?  Are the tones fluctuating in loudness?  Press the tone button, do you hear a loud click before hearing the tone?  Increase and decrease the volume, does the loudness increase and decrease?  When presenting the tone to the right ear, do you also hear it in the left ear (you should not)?  Does the patient response button work?  Are the various cables and cords plugged in as they should be?

If problems are suspected, call your service provider.  Most of these issues can be addressed over the phone, but some issues will require professional repair.

I have an extra pair of headphones.  Can I use them?

Do not swap the headphones!  Headphones have different response characteristics.  Because the audiometer is calibrated for a specific pair of headphones, swapping the headphones can produce inaccurate hearing tests.  A better idea is to contact your service provider apprising them of the problem.  They will assist you to determine the best course of action.

Are there other things I can do to take care of the audiometer?

Yes, indeed.  The following are recommended:

• Plug the audiometer into a surge protector, not directly into a wall outlet
• Dust is the enemy! Cover the audiometer when not in use to keep dust out
• Organize the cords so that they are not crimped, or dragging on the floor where they could be accidentally damaged during cleaning and vacuuming
• Keep liquids away from the audiometer
• Keep a spare patient response button - this is usually the part that breaks first
• Use disposable earphone cushions for infection control to make the cushions last longer
• Use contact cleaner to periodically clean the jacks and the jack panel. Many a problem has been solved with this simple cleaning
• Keep spare batteries nearby for the bio-acoustic simulator. A leading cause of biological calibration values exceeding ± 10 dB is a weak battery.

How often does OSHA require a sound booth to be calibrated?

OSHA requires that the audiometric testing room - which can be an open room - be no louder than the maximum permissible ambient noise levels specified in the OSHA Noise Standard.  These noise levels are:

As a practical matter, it is not difficult to meet these numbers in a reasonably quiet and distraction-free room.  However, there is near universal agreement among professional hearing conservationists that these maximum permissible noise levels are too high, particularly for persons with hearing loss who often have difficulty with background noise interfering with audiometric testing.  Voluntary compliance with the more stringent criteria set forth in ANSI S3.1-1999 is recommended when feasible.  These noise levels are:

So back to the question:  how often does OSHA require measurement of background noise levels?  The answer is once, then again if something changes.

So what might change?

Relocating the booth, for one, but there is room for judgment.  If the booth is moved from one corner of the room to another, there may be no need to re-measure the background noise levels unless there is reason to believe that the noise levels are higher in the new location.

Practically, what will change the most over time is the booth itself - it will get older.  This means that the seal around the door will eventually degrade letting more sound into the booth.  More importantly, the ventilation fan will grow noisier over time and eventually need replacement.  The fans are not expensive, but can be tricky to replace.  Please have your local maintenance person give it a try as a non-ventilated sound booth can become uncomfortably warm and "stuffy" in short order.  A claustrophobic person will certainly be uncomfortable in a non-ventilated sound booth.

Bear in mind that ventilation is a major noise source when testing in an open room.  Be sure to test the background noise levels with the air conditioning/heating system on and off.  Background noise levels may be too high when the AC or heat is running.

For these reasons, it is recommended that background noise levels be measured at least every two years.  The technician providing an on-site audiometer calibration will have the necessary equipment (a rather expensive sound level meter with an octave-band analyzer) to conduct this background noise measurement.

I use a mobile service provider for annual audiometric testing.  Are they required to check background noise levels?

OSHA requires that all audiometric testing done for the purpose of compliance with the OSHA Noise Standard must be conducted in an environment where background noise levels do not exceed the maximum permissible (see the first chart above).  Mobile service providers must verify that background noise levels do not exceed the maximum, and must do this at each location where testing takes place.

Mobile services

What about documentation?

Important!  Acoustic and exhaustive audiometer calibrations must be documented on a form listing the specific functions tested and the results.  Similarly, background noise levels in the audiometric testing room must be documented as well.  This documentation is required by the OSHA Noise Standard and can be important in other legal proceedings (Workers' Compensation, for instance).

The daily biological calibration and self-listening checks should also be documented.  This provides evidence that the audiometer functioned appropriately the day of the test.

How long should you keep these documents?  The recommended time is 30 years plus the employees time at the company- as these documents could be used in Workers' Compensation cases involving long-term employees.

Can I do my own audiometer calibrations and testing room background noise level checks?

Certainly, you can and should do the daily listening checks described above.

There are no regulatory requirements stipulating who can and cannot do acoustic/exhaustive audiometer calibrations and background noise level checks in the audiometric testing room.  Anyone can do it with proper training and the right equipment.  The real issue is the cost of the equipment.  An audiometer calibration kit can easily run five times the cost of the audiometer.  Practically, only manufacturers and service providers doing many calibrations annually find it affordable to spend this much money on audiometer calibration equipment and to pay the cost associated with having that equipment calibrated annually.

Does Workplace INTEGRA provide these services?

Yes.  On-site exhaustive audiometer calibration checks and audiometric testing room background noise level checks are provided by:

• A licensed and certified Occupational Audiologist during the annual Audiologist Plant Visit, if this service is contracted
• A Technician for clients not receiving an Audiologist Plant Visit. For on-site services, see our website for our geographic service area: calibration services

Alternatively, audiometers can be shipped to our offices in Greensboro, NC or Indianapolis, IN for an exhaustive calibration check.  Request this service

Workplace INTEGRA can also provide replacement components such as patient response buttons, various cables, and earphone cushions. Audiometric testing equipment